1. Field of the Invention
The present invention relates to a sheet transport device and sheet transport method for use in image forming apparatuses such as copiers, scanners, facsimile machine and the like.
2. Description of the Related Art
Document transport devices installed in image processing apparatuses having both a document feeding tray and a document discharge tray disposed above the platen of the image reading unit of the image processing apparatus are hereinafter referred to as "wingless-type document transport devices." Furthermore, document transport devices having at least one tray among the document feeding tray and the document discharge tray which protrudes from the area above the platen are hereinafter referred to as "wing-type document transport devices." The wingless-type document transport device is advantageous in that it has a smaller footprint so as to more effectively utilize space compared to the wing-type document transport device.
Document transport systems can be classified from the perspective of the document feeding sequence into "first page systems" wherein a plurality of document pages are fed from the first page, and "last page systems" wherein the last page of the plurality of document pages is fed first. When comparing the first page system and the last page system, there is no problem using either system in copiers which simply make copies, but the first page system is desirable in apparatuses which process read information in the reading sequence as is the case in scanners and facsimile machines.
The wingless-type document transport devices invert front-to-back a document placed on the document feed tray and feed the document to the image reader unit, then again invert the document back-to-front after the image is read and eject the document to a document discharge tray. Accordingly, disadvantages arise when using the first page system. Specifically, when automatically reading a plurality of one-sided documents, the plurality of one-sided documents are stacked on a document tray with the document surface facing upward, and the uppermost document is fed sequentially from the first page. The documents which have been read are sequentially ejected to the document discharge tray with the document surface face upward. As a result the first page document becomes the lowermost document in the stack with the document surface facing upward. For this reason the operator must re-order the sequence of the documents after the documents have been read.